An analysis of 33 cases of children suffering from hyper-insulinism as a result of islet cell dysregulation is presented. Twenty-two children presented in the first 3 days after birth with the classical symptoms of hypoglycaemia. A second peak appeared between the ages of 4 months and 2 years after birth, hyperinsulinism becoming increasingly uncommon with advancing age. A logical approach to the diagnosis is presented based on an understanding of the metabolic effects of hyperinsulinism in causing hypoketonaemic hypo-fattyacidaemic hypoglycaemia. An analysis of the management of these cases is also presented It is concluded that the diagnosis of hyperinsulinism in infancy and childhood is relatively easy to make, and that a careful and logical plan of management should prevent the high incidence of neurological damage which has been reported previously in survivors.